1. Field of the Invention
The present invention is directed to a method and a device for internally cleaning an implanted infusion system, of the type having an infusion pump connected on its outlet side to a catheter via a nonreturn valve, a flushing port also being provided downstream of the nonreturn valve and upstream of the catheter, with a flow of cleaning fluid being passed through the infusion pump and the nonreturn valve.
2. Description of the Prior Art
Implantable infusion systems or infusers deliver medication or drugs usually in liquid form, such as an insulin solution, to the patient. For example, such an infuser can include a drug reservoir, a micropump with a nonreturn valve (i.e., a one-way valve, which permits fluid to flow away from the micropump but which blocks a return flow) and a catheter. A problem in such known infusers is that medication can become deposited on the interior surfaces of the pump and the nonreturn valve. A reduced volume delivered per pump stroke, valve leakage etc. are some of the disruptions which then can occur. If such a disruption occurs, the deposits in the system can be dissolved and the pump performances restored. For example, the reservoir can be filled with some type of cleaning or washing liquid which dissolves the deposits in question and allows the liquid to pass through the pump by activating the pump function. Since the washing liquid can be aggressive, toxic or unapproved as a drug etc., it is important to prevent the liquid from being pumped out of the catheter and coming into contact with body tissues. Allowing dissolved drug deposits to enter the body is also inappropriate, since this can cause immune reactions. For example, denatured insulin in the abdominal cavity can give rise to the formation of antibodies, and the patient can ultimately develop resistance to insulin. Therefore, no flow of washing liquid out of the catheter is desirable during the washing operation. An influx of body fluid into the catheter is similarly not desirable. Body fluids contain proteins which can Contribute to catheter blockage and contamination of the so-called flushing port preceding the catheter. The presence of body fluid in this part of the infuser can have an adverse effect on the drug and on the life of the infuser.
In insulin pumps, this problem has hitherto been ignored and the patient has been exposed to unacceptable risks by pumping corrosive fluids out into the abdominal cavity of the patient or the following procedure has been used:
A drain, consisting of a liquid-filled flexible tube, is connected via a cannula to the flushing port with its other end positioned at a level lower than the tip of the catheter. As a result of the siphon effect, any free fluid in the abdominal cavity then flows back through the catheter out into the drain. Pumped washing liquid, often pumped with intermittent pump strokes, will then be distributed between the catheter and the drain in a ratio determined by the transient flow resistances. In favorable conditions, the quantity of washing liquid exiting through the catheter will be returned to the drain because of the retrograde siphon flow of body fluid in the catheter. This known method, however, has several major weaknesses.
Usually there is very little free liquid in the abdominal cavity, and any liquid therein is highly viscous. Since the interior lumen of the catheter is very small, typically 0.3 mm in diameter, the generation of an appreciable retrograde flow is uncertain. Moreover, there is a risk that the tip of the catheter becomes pressed against body tissue in the abdominal cavity, thereby preventing any retrograde flow, under such circumstances, however, it still will allow forward flow because an increase in the catheter pressure momentarily lifts the catheter tip. Thus, under certain circumstances, a valve function can develop in the catheter orifice, and there could be an outflow of hazardous substance into the abdominal cavity, despite the drainage provided.
Thus, the prior art methods provide neither desired control of the procedure nor patient safety.